1. Field of the Invention
The invention relates to catalytic reduction of oxides of nitrogen, NO.sub.x, produced in catalytic cracking unit regenerators operating in complete CO combustion mode.
2. Description of Related Art
NO.sub.x, or oxides of nitrogen, in flue gas streams from FCC regenerators operating in complete CO burn mode is a pervasive problem. FCC units process heavy feeds containing nitrogen compounds, and much of this material is eventually converted into NO.sub.x emissions. There may be some nitrogen fixation, or conversion of nitrogen in regenerator air to NO.sub.x, but most of the NO.sub.x in the regenerator flue gas is believed to come from oxidation of nitrogen compounds in the feed.
Several powerful ways have been developed to deal with the problem. The approaches fall into roughly five categories:
1. Feed hydrotreating, to keep NO.sub.x precursors from the FCC unit.
2. Segregated cracking of fresh feed.
3. Process approaches which reduce the amount of NO.sub.x formed in a regenerator via regenerator modifications.
4. Catalytic approaches, using a catalyst or additive which is compatible with the FCC reactor, which suppress NO.sub.x formation or catalyze its reduction.
5. Stack gas cleanup methods which are isolated from the FCC process.
The FCC process will be briefly reviewed, followed by a review of the state of the art in reducing NO.sub.x emissions, and hydrothermal catalyst deactivation.